6 SEDIMENT QUALITY Chapter 6 – Sediment 6.1 Sediments in the sea bottom are often regarded as the ultimate sink of pollutants in the marine environment. They are also an important habitat for a variety of marine life, including ecologically and commercially important species. The organic and inorganic pollutants accumulated in sediments may pose a potential threat to marine organisms and human health, and therefore need to be monitored regularly. 6.2 In 2004, the Environmental Protection Department (EPD) monitored marine sediments twice, at 45 stations in open waters (Figure 1.3) and 15 stations in typhoons shelters (Figure 1. 4). Sediment samples were collected using a grab sampler. Field measurements, e.g. electrochemical potential, were done on board the monitoring vessel and laboratory tests were conducted on over 60 physical, chemical and biological parameters (Table 1.3). A summary of the marine sediment quality in the territory in the past 5 years (2000–2004) is shown in Tables 6.1–6.6. 6.3 The marine sediments in Hong Kong consist mainly of silt. The sediments in the eastern waters, in particular the deeper and inshore water of Mirs Bay, are of a finer consistency, with 90% (w/w) of the sediment particles below the size of 63µm (Figure 6.1). In areas with stronger currents such as the North Western water and Victoria Harbour, the sediment particles are coarser and only about 40-80% of the particles are smaller than 63µm. 6.4 The marine sediments in Hong Kong are generally anoxic, i.e. with negative electrochemical potential. Highly anoxic sediments (below -300mV) were found in the Victoria Harbour WCZ (-326mV to -363mV), inner Mirs Bay, i.e. Double Haven and Crooked Harbour (-326mV to -358mV), and Tolo Harbour (-310mV to -324mV) as shown in Figure 6.2. The low electrochemical potential in Victoria Harbour was mainly related to organic deposition from effluent discharges. Double Haven and Crooked Harbour in Mirs Bay and Tolo Harbour had many fish culture zones (Figure 1.6). Sediments in these areas were subject to the long-term effects of organic pollution from fish excreta, fishfeed and other sources. 6.5 In assessing contamination of marine sediments by contaminants, guideline values in the ‘Environment, Transport and Work Bureau Technical Circular ETWB(W) No. 34/2002 - MARINE WATER QUALITY IN HONG KONG IN 2004 P 6.2 6 SEDIMENT QUALITY Management of Dredged / Excavated Sediment’ were used as bench marks. The Upper Chemical Exceedance Levels (UCELs) and Lower Chemical Exceedance Levels (LCELs) of 12 individual or groups of chemical contaminants are shown in Table 6.7. Metals, Metalloid and Trace Organics 6.6 Sediments in Victoria Harbour (VS3, VS5 and VS6), Junk Bay (JS2) and Tsuen Wan Bay (VS9 and VS10) had higher levels of heavy metals, in particular copper and silver, which exceeded the UCELs (Figures 6.3 and 6.5). This was likely to be related to discharges from printed circuit board, electroplating industries and photo-developing business in the old industrial areas i.e. Kwun Tong, To Kwa Wan, Yau Tong and Tsuen Wan between the 60s and 80s. Mercury in marine sediments was generally low except at one station (VS6) in western Victoria Harbour where the level exceeded the UCEL (Figure 6.4). Mercury contamination may be related to the former discharges from dental clinics and industries. 6.7 Among the trace organic pollutants, the levels of polychlorinated biphenyls (PCBs) in the marine sediments of Hong Kong were generally low, below the LCEL except at VS6 (Figure 6.6). The 18 PCB congeners in over 90% of the sediment samples were below the reporting limits (<2µg/kg dry weight). Eight PCB congeners (i.e. PCB 101, 118, 128, 138, 153, 170, 180 and 187) were detected in central and western Victoria Harbour (VS5, VS6, VS9 and VS10). The levels of low and high molecular weight PAHs in the marine sediment samples were mostly below the LCELs with the exception of one station in western Victoria Harbour (VS6) where high molecular weight PAHs exceeded the LCEL (Figures 6.7 and 6.8). MARINE WATER QUALITY IN HONG KONG IN 2004 P 6.3 6 SEDIMENT QUALITY Figure 6.1 Particle Size Fractionation <63 µm in marine sediments in Hong Kong, 2000 – 2004 Shenzhen N Particle Size Fractionation <63µm MS3 (%w/w) MS4 MS1 MS2 >80 MS7 MS5 40 - 80 MS17 DS1 <40 DS2 TS5 DS3 MS6 TS3 TS4 MS16 New Territories DS4 TS2 NS4 PS3 VS10 MS15 NS3 NS2 PS5 Kowloon VS9 NS6 WS1 PS6 VS6 VS3 JS2 VS5 MS14 ES4 Hong Kong Island Lantau Island ES1 SS5 WS2 ES2 SS2 SS4 SS6 SS1 MS13 MS8 SS3 0510km Figure 6.2 Electrochemical potential in marine sediments in Hong Kong, 2000 - 2004 Shenzhen Electrochemical N potential (mV) MS3 below -300 MS4 MS1 MS2 -201 to -300 MS7 MS5 -101 to -200 MS17 DS1 0 to -100 DS2 TS5 DS3 MS6 TS3 TS4 MS16 New Territories DS4 TS2 NS4 PS3 VS10 MS15 NS3 NS2 Kowloon PS5 VS9 NS6 WS1 PS6 VS6 VS3 JS2 VS5 MS14 ES4 Hong Kong Island Lantau Island ES1 SS5 WS2 ES2 SS2 SS4 SS6 SS1 MS13 MS8 SS3 0510km MARINE WATER QUALITY IN HONG KONG IN 2004 P 6.4 6 SEDIMENT QUALITY Figure 6.3 Copper in marine sediments in Hong Kong, 2000 - 2004 Shenzhen N Copper MS3 (mg/kg dry weight) MS4 MS1 MS2 >110 MS7 MS5 66 - 110 MS17 DS1 0 - 65 DS2 TS5 DS3 MS6 TS3 TS4 MS16 New Territories DS4 TS2 NS4 PS3 VS10 MS15 NS3 NS2 PS5 Kowloon VS9 NS6 WS1 PS6 VS6 VS3 JS2 VS5 MS14 ES4 Hong Kong Island Lantau Island ES1 SS5 WS2 ES2 SS2 SS4 SS6 SS1 MS13 MS8 SS3 0510km Figure 6.4 Mercury in marine sediments in Hong Kong, 2000 - 2004 Shenzhen N Mercury MS3 (mg/kg dry weight) MS4 MS2 MS1 >1.0 MS7 MS5 0.6 - 1.0 MS17 DS1 0.0 - 0.5 DS2 TS5 DS3 MS6 TS3 TS4 MS16 New Territories DS4 TS2 NS4 PS3 VS10 MS15 NS3 NS2 PS5 Kowloon VS9 NS6 WS1 PS6 VS6 VS3 JS2 VS5 MS14 ES4 Hong Kong Island Lantau Island ES1 SS5 WS2 ES2 SS2 SS4 SS6 SS1 MS13 MS8 SS3 0510km MARINE WATER QUALITY IN HONG KONG IN 2004 P 6.5 6 SEDIMENT QUALITY Figure 6.5 Silver in marine sediments in Hong Kong, 2000 - 2004 Shenzhen N Silver MS3 (mg/kg dry weight) MS4 MS1 MS2 >2 MS7 MS5 2 MS17 DS1 0 - 1 DS2 TS5 DS3 MS6 TS3 TS4 MS16 New Territories DS4 TS2 NS4 PS3 VS10 MS15 NS3 NS2 Kowloon PS5 VS9 NS6 WS1 PS6 VS6 VS3 JS2 VS5 MS14 ES4 Lantau Island Hong Kong Island ES1 SS5 WS2 ES2 SS2 SS4 SS6 SS1 MS13 MS8 SS3 0510km Figure 6.6 Total polychlorinated biphenyls (PCBs) in marine sediments in Hong Kong, 2002 - 2004 Shenzhen N Total PCBs MS3 (μg/kg dry weight) MS4 MS1 MS2 >180 MS7 MS5 24 - 180 MS17 DS1 0 - 23 DS2 TS5 DS3 MS6 TS3 TS4 MS16 New Territories DS4 TS2 NS4 PS3 VS10 MS15 NS3 NS2 Kowloon PS5 VS9 NS6 WS1 PS6 VS6 VS3 JS2 VS5 MS14 ES4 Hong Kong Island Lantau Island ES1 SS5 WS2 ES2 SS2 SS4 SS6 SS1 MS13 MS8 SS3 0510km MARINE WATER QUALITY IN HONG KONG IN 2004 P 6.6 6 SEDIMENT QUALITY Figure 6.7 Low molecular weight polycyclic aromatic hydrocarbons (PAHs) in marine sediments in Hong Kong, 2002 - 2004 Shenzhen N Low molecular weight PAHs MS3 (μg/kg dry weight) MS4 MS1 MS2 >3160 MS7 MS5 551 - 3160 MS17 DS1 0 - 550 DS2 TS5 DS3 MS6 TS3 TS4 MS16 New Territories DS4 TS2 NS4 PS3 VS10 MS15 NS3 NS2 Kowloon PS5 VS9 NS6 WS1 PS6 VS6 VS3 JS2 VS5 MS14 ES4 Hong Kong Island Lantau Island ES1 SS5 WS2 ES2 SS2 SS4 SS6 SS1 MS13 MS8 SS3 0510km Figure 6.8 High molecular weight polycyclic aromatic hydrocarbons (PAHs) in marine sediments in Hong Kong, 2000 - 2004 Shenzhen N High molecular weight PAHs MS3 (μg/kg dry weight) MS4 MS1 MS2 >9600 MS7 MS5 1701 - 9600 MS17 DS1 0 - 1700 DS2 TS5 DS3 MS6 TS3 TS4 MS16 New Territories DS4 TS2 NS4 PS3 VS10 MS15 NS3 NS2 PS5 Kowloon VS9 NS6 WS1 PS6 VS6 VS3 JS2 VS5 MS14 ES4 Hong Kong Island Lantau Island ES1 SS5 WS2 ES2 SS2 SS4 SS6 SS1 MS13 MS8 SS3 0510km MARINE WATER QUALITY IN HONG KONG IN 2004 P 6.7 6 SEDIMENT QUALITY Table 6.1 Summary statistics of marine sediment quality of the Tolo Harbour and Channel and Southern WCZs, 2000 - 2004 Tolo Harbour and Channel Hong Kong Island West Lamma Buffer Channel Channel Harbour Subzone Subzone Subzone (South) Parameter TS2 TS3 TS4 TS5 SS1 SS2 SS3 SS4 Number of samples 10 10 10 10 10 10 10 10 72 69 63 91 71 87 73 80 Particle Size Fractionation <63µm (%w /w) (14 - 86) (43 - 85) (34 - 78) (80 - 95) (57 - 92) (74 - 92) (52 - 93) (49 - 96) -321 -310 -324 -312 -142 -147 -173 -143 Electrochemical Potential (mV) ((-376) - (-212)) ((-364) - (-183)) ((-390) - (-198)) ((-355) - (-130)) ((-205) - (-95)) ((-338) - (-32)) ((-280) - (-91)) ((-192) - (-84)) 34 34 40 30 55 47 52 46 Total Solids (%w /w ) (30 - 40) (28 - 45) (32 - 54) (28 - 35) (48 - 59) (43 - 51) (47 - 59) (42 - 51) 10.2 9.8 9.5 11.3 6.5 7.5 6.8 7.4 Total Volatile Soilds (%w /w) (8.6 - 12.0) (7.4 - 12.0) (5.0 - 12.0) (9.7 - 13.0) (5.9 - 7.6) (6.7 - 8.0) (6.0 - 7.3) (6.4 - 7.9) 24000 22000 21000 19000 11000 15000 19000 16000 Chemical Oxy gen Demand (mg/kg) (21000 - 28000) (15000 - 25000) (17000 - 23000) (16000 - 22000) (10000 - 13000) (13000 - 16000) (14000 - 25000) (14000 - 18000) 0.8 0.7 0.8 0.8 0.9 0.7 0.9 0.6 Total Carbon (%w/w) (0.7 - 0.9) (0.5 - 0.8) (0.7 - 1.0) (0.7 - 0.9) (0.6 - 1.0) (0.6 - 0.7) (0.7 - 1.4) (0.6 - 0.7) 11.2 6.2 11.6 18 6.3 11.2 6.3 4.8 Ammonical Nitrogen (mg/kg) (1.6 - 32.0) (2.1 - 14.0) (2.1 - 24.0) (6.0 - 25.0) (0.2 - 11.0) (0.4 - 37.0) (1.6 - 16.0) (0.4 - 9.6) 598 525 596 730 388 391 366 366 Total Kjeldahl Nitrogen (mg/kg) (470 - 720) (350 - 640) (460 - 820) (620 - 890) (260 - 490) (230 - 520) (240 - 460) (240 - 420) 182 165 191 207 219 193 235 193 Total Phosphorus (mg/kg) (160 - 220) (140 - 200) (140 - 230) (180 - 240) (160 - 250) (150 - 240) (200 - 270) (160 - 240) 215 167 170 175 37 52 32 49 Total Sulphide (mg/kg) (13 - 400) (30 - 320) (17 - 330) (53 - 240) (10 - 70) (8 - 100) (11 - 72) (21 - 140) 0.2 0.1 0.1 0.1 <0.1 <0.1 <0.1 <0.1